Vulcanization of rubber



United States Patent 2,713,572 VULCANIZATION 0F RUBBER George E. Hall, Jr., Wyandotte, Mich assignor to Wyandotte Chemicals Corporation, Wyandotte, Micln, a corporation of Michigan No Drawing. Application August 12, 1953, Serial No. 373,917

10 Claims. (Cl. 2607.5)

This invention relates to a method of vulcanizing conjugated diolefin type elastomers and to the vulcanizates obtained thereby. In particular, the invention relates to a method of vulcanizing conjugated diolefin type elastomers in which a thiazyl sulfide is employed as the primary accelerator and in which certain novel conjugated polyoxypropylene-polyoxyethylene compounds are included in the elastomer as an activator for the thiazyl sulfide.

In modern rubber technology, thiazyl sulfides, e. g. mercaptobenzothiazole and 2,2 benzothiazyl sulfide, are used extensively as vulcanization accelerators, and frequently one or more secondary accelerators or activators are employed in conjunction therewith. Typical examples of such activators are tetramethylthiuram disulfide, tetramethylthiuram sulfide, zinc diethyithiocarbonate, etc. cost and frequently cause overcuring of the vulcanizate, which overcuring results in poor aging properties in the vulcanizate.

-It is an object of this invention to provide a method for vulcanizing conjugated diolefin type elastomers which includes the use of an improved class of activators in conjunction with a primary thiazyl sulfide accelerator.

Another object of this invention is to provide vulcanized conjugated diolefin type elastomers having improved aging properties.

Other objects and advantages of this invention will be apparent from the following detailed description thereof.

It has been discovered that certain novel conjugated polyoxypropylene-polyoxyethylene compounds may be advantageously employed as activators for thiazyl sulfides in accelerating the vulcanization of conjugated diolefin type elastomers. The conjoint use of a thiazyl sulfide and a novel conjugated polyoxypropylene-polyoxyethylene compounds not only provides rapid vulcanization of the elastomer, but also prevents overcuring of the elastomer and thus provides a vulcanizate having improved aging properties. In addition to their performance characteristics, the conjugated polyoxypropylenepolyoxyethylene compounds are substantially lower in cost than many of the commonly used activators.

The conjugated polyoxypropylene-polyoxyethylene compounds are prepared by condensing ethylene oxide with a polyoxypropylene polymer. Sufiicient ethylene oxide is condensed with the polyoxypropylene polymer so that the oxyethylene content constitutes at least 20%, by weight, of the resultant product. Superior results are obtained when the oxyethylene content constitutes substantially more than 20% of the compound and excellent results are obtained when the oxyethylene content constitutes 90% or even more of the compound.

The Polyoxypropylene polymers, with which ethylene oxide is condensed to prepare the conjugated polyoxypropylene-polyoxyethylene compounds, are prepared by condensing propylene oxide with an organic compound containing one or a plurality of reactive hydrogen atoms. The particular structure of the conjugated olyoxypropyl- The presently used activators are high in Patented Jul Y is the residue of an organic compound containing one reactive hydrogen atom,

n has a value of at least 6, and

m has a value such that the oxyethylene groups constitute at least 20%, by weight, of the compound.

While at least six oxypropylene groups are required in the above type compounds, superior results are obtained when the conjugated polyoxypropylene-polyoxyethylene compounds contain l0-20, or even more, oxypropylene groups. A complete description of such compounds and Serial No. 229,128, filed May 31, 1951, now U. S. 2,677,700, and that description is incorporated herein by reference.

When the olyoxypropylene polymer is prepared by condensing propylene oxide with a reactive hydrogen compound containing a plurality of reactive hydrogen [B] Polyoxypropylene polymer [(C2H40)mH]w where:

The olyoxypropylene polymer is the condensation product of propylene oxide and an organic compound containing a plurality of reactive hydrogen atoms and contains at least 12 oxypropylene groups,

m is an integer,

m and x have values such that the oxyethylene groups constitute at least 20%,

by weight, of the compound.

A complete description of the compounds conforming to the above formula and their preparation is contained in copending application of Lester G. Lundsted, Serial No. 386,945, filed October 19, 1953, now U. S. 2,674,619, which description is incorporated herein by reference.

As set forth in the above mentioned application of Lester G. Lundsted, any reactive hydrogen compound containing a plurality of reactive hydrogen atoms can be used in preparing olyoxypropylene polymers of the compounds described in Formula B. In the practice of the present invention, however, especially good results are obtained when the polyoxypropylene polymer is obtained by condensing propylene oxide with an arylsulfonamide or an aliphatic diamine, e. g. ethylene diamine.

1n the above description of the conjugated polyoxypropylcnc-polyoxyethylene compounds reference was made to individual compounds containing prescribed minimum numbers of oxypropylene groups and prescribed minimum oxyethylene contents. The nature of alkylene oxide condensations is such, however, that mixtures of compounds are inevitably obtained, and the mixtures of the conjugated polyoxypropylene-polyoxyethylene compounds cannot be separated into individual compounds by known methods. Consequently, it should be recognized that the critical limits previously described are actually average values of mixtures of such compounds.

Typical of the thiazyl sulfide accelerators with which the conjugated polyoxypropylene-polyoxyethylene compounds may be employed in vulcanizing conjugated diolefin type elastomers are the following:

Mercaptobenzothiazole Zinc mercaptobenzothiazole 2,2 benzothiazyl disulfide N-cyclohexylbenzothiazyl sulfenamide 2-mercapto-4-ethylthiazole Bis 4,5 -dimethylthiazyl) sulfide Dinitrophenylbenzothiazyl sulfide Phenylaminomethyl-2-benzothiazyl sulfide it is recognized in the art that the thiazyl sulfide accelerators are effective in accelerating the vulcanization of any conjugated diolefin type elastomer. Thus, the thiazyl sulfides are used in conjunction with not only natural rubber, but with all of the diolefin synthetic rubbers such as GR-S (copolymer of butadiene 1,3 and styrene), butyl rubber (copolymer of isobutylene and butadiene 1,3), the acrylonitrile rubbers (copolymer of butadiene 1,3 and acrylonitrile), etc. The conjugated polyoxypropylene-polyoxyethylene compounds may be used in conjunction with a thiazyl sulfide in vulcanizing any of the above mentioned diolefin elastomers.

The conjugated polyoxypropylene-polyoxyethylene activators may be used alone with the thiazyl sulfides or may be used in combination with other activators for thiazyl sulfides. In many types of rubber stocks, e. g. tire-tread stocks, mechanical goods stocks, etc. it is preferred to use the conjugated polyoxypropylene-polyoxyethylene compounds as the sole activator. In other types of rubber stocks, particular where rapid cures are desired at low temperatures, e. g. in golf ball cover stocks, latex dipped goods, etc., the conjugated polyoxypropylene-polyoxyethylene compounds may be used in conjunction with other activators.

The following examples are set forth to more clearly illustrate the principle and practice of this invention to those skilled in the art.

EXAMPLE 1 Compounding ingredient:

GR-S

Zinc oxide 3 Stearic acid 2 Cumar resin Carbon black Calcium carbonate 40 Petroleum softener 8 Compounding ingredient: Parts by weight Wood rosin Sulfur 2.5 2,2 benzothiazyl disulfide 1.5 Tetramethylthiuram disulfide 0.2

Conjugated polyoxypropylene-polyoxyethylene compound Variable After press curing the stocks for 30 minutes at 287 F., the following physical properties were obtained.

Table I Modulus, p. s. i. Elonga Parts Activator tion,

300% 500% Percent In examining Table I, it will be noted that progressively higher modulus values were obtained as the content of the polyoxypropylene-polyoxyethylene compound was increased. It will also be noted that the ultimate elongation of the stocks decreased as the activator content was increased. As is apparent to those skilled in the rubber compounding part, the increase in modulus value with the concomitant decrease in ultimate elongation is evidence of a higher degree of vulcanization or cure, and definitely establishes that the conjugated polyoxypropylene-polyoxyethylene compound activates the cure of the stock.

EXAMPLE 2 The effect of activator concentration on vulcanization, when the conjugated polyoxypropylene-polyoxyethylene compound was used as the sole activator, was determined by adding varying quantities of the compound described in Example 1 to a GR-S formulation. The GRS formulation used was identical with the one shown in Example 1 except that the tetramethylthiuram disulfide was omitted. After press curing for 30 minutes at 287 F., the following physical properties were obtained:

Table II Modulus, p. s. i. Part5 Activator Tensile, Elongation,

p. s. 1. Percent No cure-.. No cure.

. No cure-..

The above results indicate that the optimum concentration of the particular conjugated polyoxypropylenepolyoxyethylene compound tested was about 0.6 part activator per parts of rubber. With other of the conjugated polyoxypropylene-polyoxyethylene compounds the optimum concentration will vary from about 0.2 part to about 0.8 part per hundred parts elastomer and acceptable results are obtained within the broader limits of from about 0.1 part to about 1.2 parts per hundred parts elastomer.

EXAMPLE 3 Four series of conjugated polyoxypropylene-polyoxyethylene compounds were evaluated in the following formulation:

Compounding ingredient: Parts by weight G R-S 1'00 vators is that they reduce the tendency of rubber stocks Z111c to overcure, which overcuring results in poor aging prop- Stearlc aclfi 2 erties. The principal effect of poor aging properties is z'umar resm 5 a loss in tensile strength. To establish the advantage of $2 33; LZi E t the conjugatedv polyoxypropylene-polyoayethylene com-. Petroleum softener 8 pounds thls. regard two vulcamzates. i prepared Wood rosin 2 and their tensile strengths were determined when. PlCr. sulfur m pared and after aging for 24 hours at 212 F. The rubbenzothiazyl disulfide 5 her formulation; used wasthe one shown in Examples II. c j d polyoxypropylene polyoxyethylene. The structure of the activators and the test results; are

compound 0.2 shown in Table IV below:

Table IV I Composition Polyoxypropylene-Polyoxyethylene Compound T u Tenssile',

T 6115 e, p. Test No. o i 'z g fir Oxyethgg i h s i l g Starting Reactive ggfli 051E219: prepared aging. Percent Hydrogen Compound oxypropyb Wt 2 F.

ene cent Polymer a H x 1 Ethylene Diamine a7- 85 2, 470 2,360 96 2 Benzenesulfonamide... 16 80 2 280 The compounds in each series differed from each other only in oxyethylene content, and the tests were designed to show the importance of this variable. The four series of compounds represented products in which the poly oxypropylene polymer was derived from four difierent' reactive hydrogen compounds. of the conjugated polyoxyp'ropylene-polyoxyethylene compound and the physical properties that were obtained after curing 90 minutes at 287 F. are shown in Table III below:

Table III i Composition Po1yoxypropylene-Polyoxyethylene Compound The specific composition the conjugated po1yoxypropylene-polyoxyethylene acti- It is seen in the above retained over- 96% sile values of over treatment. stock, except that tetramethylthiuram disulfide was used as the activator, was aged in this manner, the stock retained only 78% of its original tensile strength and had a tensile strength of only 1820 p. s. 1.

It Will be obvious to those skilled in the art that the table, that the vulcanizates of their tensile strength and had ten- 2200 p. s. i. after this drastic aging invention may be practiced with'the use of fillers; soften- Modulus, p. s. i;

Number Elonga- Test N o. Oxygropyl- Oxlyethg g? Ption, t ene roups y ene ercen Starting ggg gg g in Poly- Content, 300% 500% p oxypropyl- Wt. Perene cent Polymer l l Propylene Glycol 80 200 675 2, 260 825 2. do 30 40 I 650 2, 060 810 BR d0 30 325 750 1, 830 750 4. enzenesulfonamide 1 6 50 175 700 560 805 5 0 16 80 250 875 2,300 745 6 N-Phenyl Benzenesulfonamide 7 34 25 475 1, 780 825 7- do 7 51 600 2, 260 830 7 67 200 750 2, 340 5 57 25 150 (100 2, 360 900 37 50 675 2, 210 805 37 75 250 825 2, 090 715 37 85 300 950 2, 600 750 Zinc oxide in formula decreased to 3.0 parts; vulcanizates cured 30 min It will be noted in each of the above series that the modulus values increased as the oxyethylene content of the activator was increased It will be further noted that with the increase in modulus value there was concomitant decrease in the ultimate elongation of the vulcanizate. These results indicate that an increased activation of the thiazyl sulfide accelerator and a tighter cure were obtained as the oxyethylene content of the conjugated polyoXypropylene-polyoxyethylene was increased.

EXAMPLE 4 As noted earlier herein, an outstanding advantage of utes.

As a comparison, when an identical rubber vator being present in an amount sufficient to activate the primary accelerator.

2. A conjugated diolefin elastomer containing sulfur, a primary thiazyl sulfide accelerator and, as an activator for the thiazyl sulfide, a mixture of conjugated polyoxypropylene-polyoxyethylene compounds in which the oxyethylene content constitutes at least 20%, by weight, of the compounds and in which the polyoxypropylene portion of the compounds contains an average of at least 12 oxypropylene groups and is obtained by condensing propylene oxide with benzenesulfonamide; said activator being present in an amount sufiicient to activate the primary accelerator.

3. The composition of claim 9 in which the conjugated diolefin elastomer is a rubbery copolymer of butadiene and styrene.

4. The composition of claim 1 in which the conjugated diolefin elastomer is a rubbery copolymer of butadiene and styrene.

5. The composition of claim 2 in which the conjugated diolefin elastomer is a rubbery copolymer of butadiene and styrene.

6. The composition of claim 9 in which the conjugated diolefin elastomer is natural rubber.

7. In the method of vulcanizing a conjugated diolefin elastomer containing sulfur and a primary thiazyl sulfide which comprises heating the uncured conjugated diolefin to a vulcanizing temperature; the improvement which comprises incorporating in the conjugated diolefin elastomer from about 0.1 to about 1.2 parts (based upon 100 parts by weight of the elastomer) of a mixture of conjugated polyoxypropylene-polyoxyethylene compounds in which the oxyethylene content constitutes at least 20%, by weight, of the compounds and in which the polyoxypropylene portion of the compounds contains an average of at least 12 oxypropylene groups and is obtained by condensing propylene oxide with ethylene diamine.

8. In the method of vulcanizing a conjugated diolefin elastomer containing sulfur and a primary thiazyl sulfide which comprises heating the uncured conjugated diolefin to a vulcanizing temperature; the improvement which comprises incorporating in the conjugated diolefin elastomer from 0.1 to about 1.2 parts (based upon 100 parts by weight of the elastomer) of a mixture of conjugated polyoxypropylene-polyoxyethylene compounds in which the oxyethylene content constitutes at least 20%, by weight, of the compounds and in which the polyoxypropylene portion of the compounds contains an average of at least 12 oxypropylene groups and is obtained by condensing propylene oxide with benzenesulfonamide.

9. A conjugated diolefin elastomer containing sulphur, a primary thiazyl sulfide accelerator and, as an activator for the thiazyl sulfide, a substance selected from the group of (a) a mixture of conjugated polyoxypropylene-polyoxyethylene compounds in which the oxyethylene content constitutes at least 20%, by weight, of the compounds and in which the polyoxypropylene portion of the compounds contains an average of at least 6 oxypropylene groups and is prepared by condensing propylene oxide with an organic compound containing one reactive hydrogen atom, and (b) a mixture of conjugated polyoxypropylene-polyoxyethylene compounds in which the oxyethylene content constitutes at least 20%, by weight, of the compounds and in which the polyoxypropylene portion of the compounds contains an average of at least 12 oxypropylene groups and is prepared by condensing propylene oxide with an organic compound containing a plurality of reactive hydrogen atoms; said activator being present in an amount suflicient to activate the primary accelerator.

10. In the method of vulcanizing a conjugated diolefin elastomer containing sulphur and a primary thiazyl sulfide which comprises heating the uncured conjugated diolefin to a vulcanizing temperature; the improvement which comprises incorporating in the conjugated diolefin elastomer from about 0.1 to 1.2 parts (based upon 100 parts by weight of the elastomer) of a substance selected from the group consisting of (a) a mixture of conjugated polyoxypropylene-polyoxyethylene compounds in which the oxyethylene content constitutes at least 20%, by weight, of the compounds and in which the polyoxypropylene portion of the compounds contains an average of at leach 6 oxypropylene groups and is prepared by condensing propylene oxide with an organic compound containing one reactive hydrogen atom, and (b) a mixture of conjugated polyoxypropylene-polyoxyethylene compounds in which the oxyethylene content constitutes at least 20%, by weight, of the compounds and in which the polyoxypropylene portion of the compounds contains an average of at least 12 oxypropylene groups and is prepared by condensing propylene oxide with an organic compound containing a plurality of reactive-hydrogen atoms.

No references cited. 

1. A CONJUGATED DIOLEFIN ELASTOMER CONTAINING SULFUR, A PRIMARY THIAZYL SULFIDE ACCELERATOR AND, AS AN ACTIVATOR FOR THE THIAZYL SULFIDE, A MIXTURE OF CONJUGATED POLYOXYPROPYLENE-POLYOXYETHYLENE COMPOUNDS IN WHICH THE OXYETHYLENE CONTENT CONSTITUTES AT LEAST 20%, BY WEIGHT, OF THE COMPOUNDS AND IN WHICH THE POLYOXYPROPYLENE PORTION OF THE COMPOUNDS CONTAINS AN AVERAGE OF AT LEAST 12 OXYPROPYLENE GROUPS AND IS OBTAINED BY CONDENSING PROPYLENE OXIDE WITH ETHYLENE DIAMINE; SAID ACTIVATOR BEING PRESENT IN AN AMOUNT SUFFICIENT TO ACTIVATE THE PRIMARY ACCELERATOR. 